Back for a seating unit



FIG. 1 is a front perspective view of a chair back embodying the present design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a front view thereof;

FIG. 6 is a rear view thereof;

FIG. 7 is a top view thereof; and,

FIG. 8 is a bottom view thereof. 

The ornamental design for a back for a seating unit, as shown and described. 